The present invention relates to a digital video tape recorder and, more particularly, to apparatus and method for recording and reproducing high priority digital video data of an advanced television (ATV) signal in areas of a track which are reproduced in high-speed reproducing modes.
Existing analog video recorders record analog video signals on a magnetic medium generally in non-compressed form since their bandwidths are quite narrow. In addition to recording and reproducing video signals, current analog video recorders are operable to reproduce the stored video signals in a high-speed search mode, whereat the magnetic tape medium is transported at a greater speed than the speed at which the tape is transported during normal reproduction. Since positions on each recording track on the magnetic tape medium correspond to positions in a video image, partial scannings of a multiple number of tracks produce sufficient information to produce a recognizable, albeit, poor image.
Digital video recorders, such as digital VTRs, have been developed for recording a video signal in digitized form on a magnetic medium. However, since the bandwidth of a digital video signal is quite wide, it is difficult to record a digital video signal directly on a video tape. Hence, techniques have been proposed for encoding the digital video signal in a manner which reduces its bandwidth. So-called compression encoding techniques include the orthogonal transformation and variable length encoding of the digital video signal; and one highly efficient encoding technique utilizes discrete cosine transformation, or DCT. Compression encoding is further described in U.S. Pat. Nos. 5,321,440 and 5,346,310, and U.S. patent application Ser. No. 07/967,015, the disclosure of which are incorporated herein by reference.
Digital VTRs which utilize compression encoding techniques to reduce the bandwidth of television signals, e.g., NTSC signals or HDTV signals, prior to recording also decompress or decode reproduced signals so as to return the compressed television signals to their original non-compressed form. One efficient compression technique is to combine the above-mentioned DCT with motion compensation, which utilizes both intraframe coding and interframe coding of the video signal. However, and in contrast to high-speed reproduction of analog signals by an analog video recorder, digital VTRs may not simply scan the tracks on a magnetic tape while transporting it at a greater speed to produce high-speed reproduced images since DCT and interframe decompression techniques require a substantial part, if not all of the data on each track to be reproduced in order to produce stable video images. For example, positions of discrete cosine transformed digital video data do not coincide with positions in a video image, and thus, scanning a different portion of a multiple number of tracks will not produce data pertaining to respectively different portions of an image. In addition, an image, or a portion of an image, may not be produced from the reproduction of a track (or a portion of that track) in which interframe coded data is stored since such data has meaning only with respect to previously stored intraframe or interframe coded data, and since only a portion of each track is reproduced, only a portion of an image, at best, may be produced.